1. Field of the Invention
The present invention relates to a light-emitting semiconductor device that emits blue light and uses a group III nitrogen compound. Especially, the invention is about a light-emitting semiconductor device that emits purer blue color.
2. Description of the Prior Art
A gallium nitride (GaN) compound semiconductor with a p-n junction has been used to obtain a light-emitting diode (LED) which emits blue light. This semiconductor device is useful because of its high luminous efficiency resulting from direct electron transition and because of its ability to emit blue light, which is one of the three primary colors.
The "a" and "c" planes of semiconductors, rotate at an off angle, or just substrates, have been utilized as epitaxial growth plane of to form GaN compound semiconductor with smoother surface.
However, the luminous condition of a p-layer which is regarded as an emission layer of an LED grown on the just substrate is a group of luminous dots. This is attributed to non-uniform impurity doping of magnesium (Mg) into the emission layer. Consequently, an LED with the just substrate has poor luminous intensity.